It is common in the electronic industry to secure various electronic components (e.g., semiconductor chips or devices) to flexible plastic strips or tape for handling and testing prior to eventual packaging of such components in the ultimate product (e.g., calculator or other product utilizing electronic components). For example, individual electronic components such as semiconductor chips or integrated circuit chips (sometimes referred to as dies) are commonly secured to lead frames comprising a plurality of conductive metal leads bonded to an insulating plastic substrate (such as polyimide).
The flexible plastic substrate is in strip form (sometimes referred to as a tape) and may vary in width from less than one inch to several inches wide depending upon both the size of the individual dies to be mounted and the desired size of the lead frame. The plastic strip may be many feet long, with many replications of the lead frames thereon.
Because the plastic strip is thin and quite flexible, it may be easily and conveniently wound upon reels for storage and handling For example, the strip is drawn off from a reel to enable the individual dies to be secured to successive lead frame patterns on the strip in accordance with known techniques. Then the strip is again wound onto a reel (normally with a plastic liner fed onto the reel also to prevent contact of the dies on the strip from the other adjacent layers of the strip).
In the processing and testing of the dies on the strip or tape, the tape normally must be passed over various idler pulleys, sprockets and guides in order to achieve proper movement, alignment, direction and tension on the tape. Unfortunately, as the tape passes over such pulleys an electrostatic charge can build up on the tape and pulleys, sprockets or guides. This is undesirable. If the electrostatic charge reaches too high a level it poses a serious risk to the dies which are mounted on the tape. In the event that the electrostatic charge on the tape, pulley, sprocket or guide reaches a level of about 100 volts there is the danger of the charge damaging or destroying one or more dies on the tape if the charge should be drained rapidly through the tape
Although electrostatic charge build-up on the tape could be prevented by using electrically conductive pulleys, sprockets, and guides which are connected to ground, this would interfere or prevent testing of the electronic components (i.e., dies) mounted on the tape. The opposite edges of the tape may include special purpose voltage or ground rails. They must not be grounded or connected to each other because this would skew test results. In order for proper testing of the dies to be done, therefore, the opposite sides of the tape must be electrically isolated from each other. The presence of an electrically conductive pulley, sprocket or guide is inconsistent with the required electrical isolation. A directly grounded conductive pulley, sprocket, or guide might also cause the electrostatic charge to be discharged too rapidly, thereby causing damage to the die.
There has not heretofore been provided an electrostatic discharge protection system of the type described in connection with the present invention.